Genetic Inheritance and Genetic Data
Eric C. Anderson
The Wildlife Society CKMR Workshop, Sunday November 6, 2022
The word “locus” in genetics, much like the word “gene” has been applied to a lot of things.
For our purposes, we will use it to refer to a “chunk” of DNA that is defined by its position in the genome.
For example, around base position X on Chromosome 3:
When gametes are formed, the two copies of each locus segregate so that each gamete carries exactly one copy of each locus.
Since individuals are formed by the union of gametes, this dictates the segregation of DNA to offspring:
Consider the case of the maternal allele segregated to an offspring, in the pedigree to the right.
\(\mathrm{Probability} = \frac{1}{2}\)
\(\mathrm{Probability} = \frac{1}{2}\)
“The gene copy that gets segregated to a gamete/offspring at one locus is independent of the gene copy that gets segregated at another locus.”
When two loci are on the same chromosome they are referred to as “physically linked”
AND, they do not segregate independently.
A pair of non-inbred diploid individuals can share 0, 1, or 2 gene copies IBD at a locus.
Each possible relationship between two non-inbred individuals can be characterized by the expected fraction of the genome at which the two individuals share 0, 1, or 2 gene copies IBD. \[ \boldsymbol{\kappa}= (\kappa_0, \kappa_1, \kappa_2) \]
These are also the marginal probabilities that a pair of individuals share 0, 1, or 2, gene copies at a single locus.
Sometimes called “Cotterman coefficients”, we will call them “kappas”
These are not the coefficient of relationship or coefficient of consanguinity. (Those are not sufficient).